Image reading apparatuses, which scan image data of a document by a CIS (Contact Image Sensor), CCD (Charge Coupled Device), or other image sensor, have been known. Among the type of image reading apparatuses, for example, JP-A-6-141143 discloses a well-known image reading apparatus has both a moving document reading function and a stationary document reading function. The moving document reading function is to continuously scanned a document transferred (a moving document) in a process by use of a document transfer system, so-called an ADF (Auto Document Feeder). The stationary document reading function is to scan an image of a document (stationary document), placed on an upper surface of a main apparatus unit, by scanning a surface of the document.
Image reading by the stationary document reading function is performed as follows. That is, a document is placed on a stationary document reading glass (referred to hereinafter as “second glass”) and is pressed onto the front face of the second glass by a document cover. With the document thus being put in the stationary state, the image reading unit scans the surface of the stationary document while moving onto a back surface of the second glass in a width direction of the apparatus to read an image of the stationary document.
In performing image reading by the stationary document reading function, a book, magazine, or other book-like document (referred to hereinafter as “book document”) is placed on the second glass, a central portion of the second glass is deformed downward by the weight of the book document. In a case where an image of a double-page spread of a book, magazine, or other book-like document is to be read, a user presses the book document strongly onto the second glass in order to prevent the forming of a shadow at a central portion of the double-page spread. The second glass near a center in the depth direction of the apparatus is deformed downward by such a pressing act as well. Such deflection of the second glass obstructs the reading operation by the image reading unit and is a cause of degradation of the image quality of the read image. The back surface of the second glass may also contact the image reading unit and the image reading unit may be damaged thereby.
JP-A-11-289430 discloses an image reading apparatus, having a contact preventing means that keeps fixed an interval between a document base glass (serving as the above-described second glass) and a reading unit (serving as the above-described image reader) and thereby prevents contacting of the document base glass with the reading unit even when the document base glass becomes deformed.